System for allocating channels in a multi-radio wireless lan array

ABSTRACT

A channel allocation system for allocating channels in a frequency band to a plurality of radios in close proximity so as to minimize co-channel interference. One method for allocating channels involves initially tuning each of the plurality of radios to the same one of the plurality of channels. All of the radios then receive signals from whatever sources and a signal score is determined for each radio. The radios are then tuned to another one of the plurality of channels. The steps of receiving a signal and determining a signal score for each radio are repeated for each of the remaining channels until all channels have been used. The signal scores are then tested against a table of mapping schemes to determine maximum isolation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 11/816,065 titled “SYSTEM FOR ALLOCATING CHANNELSIN A MULTI-RADIO WIRELESS LAN ARRAY”, filed on May 13, 2008 by inventorsDirk I. Gates and James T. Mathews, the contents of which areincorporated herein by reference in its entirety.

This application further claims priority of the following provisionalpatent applications:

-   -   1. Prov. App. Ser. No. 60/660,171, titled “Wireless LAN Array,”        by Dirk I. Gates, Ian Laity, Mick Conley, Mike de la Garrigue,        and Steve Smith, filed on Mar. 9, 2005;    -   2. Prov. App. Ser. No. 60/660,276, titled “Wireless LAN Array,”        by Dirk I. Gates, Ian Laity, Mick Conley, Mike de la Garrigue,        and Steve Smith, filed on Mar. 9, 2005;    -   3. Prov. App. Ser. No. 60/660,375, titled “Wireless Access        Point,” by Dirk I. Gates and Ian Laity, filed on Mar. 9, 2005;    -   4. Prov. App. Ser. No. 60/660,275, titled “Multi-Sector Access        Point Array,” by Dirk I. Gates Ian Laity, Mick Conley, Mike de        la Garrigue, and Steve Smith, filed on Mar. 9, 2005;    -   5. Prov. App. Ser. No. 60/660,210, titled “Media Access        Controller For Use In A Multi-Sector Access Point Array,” by        Mike de la Garrigue and Drew Bertagna filed on Mar. 9, 2005;    -   6. Prov. App. Ser. No. 60/660,174, titled “Queue Management        Controller For Use In A Multi-Sector Access Point Array,” by        Mike de la Garrigue and Drew Bertagna filed on Mar. 9, 2005;    -   7. Prov. App. Ser. No. 60/660,394, titled “Wireless LAN Array,”        by Dirk I. Gates, Ian Laity, Mick Conley, Mike de la Garrigue,        and Steve Smith, filed on Mar. 9, 2005;    -   8. Prov. App. Ser. No. 60/660,209, titled “Wireless LAN Array        Architecture,” by Dirk I. Gates, Ian Laity, Mick Conley, Mike de        la Garrigue, and Steve Smith, filed on Mar. 9, 2005;    -   9. Prov. App. Ser. No. 60/660,393, titled “Antenna Architecture        of a Wireless LAN Array,” by Abraham Hartenstein, filed on Mar.        9, 2005;    -   10. Prov. App. Ser. No. 60/660,269, titled “Load Balancing In A        Multi-Radio Wireless Lan Array Based On Aggregate Mean Levels,”        by Mick Conley filed on Mar. 9, 2005;    -   11. Prov. App. Ser. No. 60/660,392, titled “Advanced Adjacent        Channel Sector Management For 802.11 Traffic,” by Mick Conley        filed on Mar. 9, 2005;    -   12. Prov. App. Ser. No. 60/660,391, titled “Load Balancing In A        Multi-Radio Wireless Lan Array Based On Aggregate Mean Levels,”        by Shaun Clem filed on Mar. 9, 2005;    -   13. Prov. App. Ser. No. 60/660,277, titled “System for        Transmitting and Receiving Frames in a Multi-Radio Wireless LAN        Array,” by Dirk I. Gates and Mike de la Garrigue, filed on Mar.        9, 2005;    -   14. Prov. App. Ser. No. 60/660,302, titled “System for        Allocating Channels in a Multi-Radio Wireless LAN Array,” by        Dirk I. Gates and Kirk Mathews, filed on Mar. 9, 2005;    -   15. Prov. App. Ser. No. 60/660,376, titled “System for        Allocating Channels in a Multi-Radio Wireless LAN Array,” by        Dirk I. Gates and Kirk Mathews, filed on Mar. 9, 2005; and    -   16. Prov. App. Ser. No. 60/660,541, titled “Media Access        Controller For Use In A Multi-Sector Access Point Array,” by        Dirk I. Gates and Mike de la Garrigue, filed on Mar. 9, 2005.

This application further claims priority to the following PCT patentapplications:

-   -   1. PCT patent application no. PCT/US2006/008747, titled “Antenna        Architecture of a Wireless LAN Array,”    -   2. PCT patent application no. PCT/US2006/008743, titled        “Wireless LAN Array,” filed on Mar. 9, 2006, which claims        priority to the above provisional patent applications;    -   3. PCT patent application no. PCT/US2006/008696, titled        “Assembly and Mounting for Multi-Sector Access Point Array,”        filed on Mar. 9, 2006;    -   4. PCT patent application no. PCT/US2006/08698, titled “System        for Allocating Channels in a Multi-Radio Wireless LAN Array,”        filed Mar. 9, 2006; and    -   5. PCT patent application no. PCT/US2006/008744, titled “Media        Access Controller for use in a Multi-Sector Access Point Array,”        filed on Mar. 9, 2006.

All of the above-listed US patent applications, US provisional patentapplications, and PCT applications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to wireless data communication systems and moreparticularly to systems and methods for providing access points inwireless local area networks.

2. Description of the Related Art

The use of wireless communication devices for data networking is growingat a rapid pace. Data networks that use “WiFi” (“Wireless Fidelity”) arerelatively easy to install, convenient to use, and supported by the IEEE802.11 standard. WiFi data networks also provide performance that makesWiFi a suitable alternative to a wired data network for many businessand home users.

WiFi networks operate by employing wireless access points to provideusers having wireless (or ‘client’) devices in proximity to the accesspoint with access to data networks. The wireless access points contain aradio that operates according to one of three standards specified indifferent section of the IEEE 802.11 specification. Radios in accesspoints communicate using omni-directional antennas in order tocommunicate signals with wireless devices from any direction. The accesspoints are then connected (by hardwired connections) to a data networksystem that completes the users' access to the Internet.

The three standards that define the radio configurations are:

-   -   1. IEEE 802.11a, which operates on the 5 GHz band with data        rates of up to 54 Mbps;    -   2. IEEE 802.11b, which operates on the 2.4 GHz band with data        rates of up to 11 Mbps; and    -   3. IEEE 802.11g, which operates on the 2.4 GHz band with data        rates of up to 54 Mbps.

The 802.11b and 802.11g standards provide for some degree ofinteroperability. Devices that conform to 802.11b may communicate with802.11g access points. This interoperability comes at a cost as accesspoints will incur additional protocol overhead if any 802.11b devicesare connected. Devices that conform to 802.11a may not communicate witheither 802.11b or g access points. In addition, while the 802.11astandard provides for higher overall performance, 802.11a access pointshave a more limited range due to their operation in a higher frequencyband.

Each standard defines ‘channels’ that wireless devices, or clients, usewhen communicating with an access point. The 802.11b and 802.11gstandards each allow for 14 channels. The 802.11a standard allows for 12channels. The 14 channels provided by 802.11b and g include only 3channels that are not overlapping. The 12 channels provided by 802.11aare non-overlapping channels. The FCC is expected to allocate 11additional channels in the 5.47 to 5.725 GHz band.

Access points provide service to a limited number of users. Accesspoints are assigned a channel on which to communicate. Each channelallows a recommended maximum of 64 clients to communicate with theaccess point. In addition, access points must be spaced apartstrategically to reduce the chance of interference, either betweenaccess points tuned to the same channel, or to overlapping channels. Inaddition, channels are shared. Only one user may occupy the channel atany give time. As users are added to a channel, each user must waitlonger for access to the channel thereby degrading throughput.

As more and more users utilize access points for service, there is aneed to increase the number of clients served by each access point andto maintain throughput even as the number of clients is increased.

SUMMARY

In view of the above, an example of a method consistent with the presentinvention is a method for allocating channels in a wireless accessdevice having a plurality of radios capable of operating on a pluralityof channels. Each channel has a frequency band with a center frequency.Each center frequency is spaced at equal frequency intervals within alarger frequency band. Any one channel may have at least one adjacentchannel located in the next frequency band. The method includesallocating one of the plurality of channels to each one of the pluralityof radios, where each of the allocated channels is not adjacent to anyone of the other allocated channels.

Other systems, methods, features and advantages of the invention will beor will become apparent to one with skill in the art upon examination ofthe following figures and detailed description. It is intended that allsuch additional systems, methods, features and advantages be includedwithin this description, be within the scope of the invention, and beprotected by the accompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

The components in the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.In the figures, like reference numerals designate corresponding partsthroughout the different views.

FIG. 1 is a block diagram of a network that uses a wireless accessdevice.

FIG. 2 is a block diagram of a transceiver module in the wireless accessdevice in FIG. 1.

FIG. 3 is a block diagram of a controller in the wireless access deviceshown in FIG. 1.

FIG. 4 is a diagram illustrating the formation of sectors by thewireless access device of FIG. 1.

FIGS. 5A-E are diagrams illustrating examples of coverage patternsformed by an example of the wireless access device of FIG. 1.

FIG. 6A is a diagram of a wireless access device of FIG. 1 labeled byradio type and number.

FIG. 6B shows coverage patterns formed by the different radio types onthe wireless access device.

FIG. 7 illustrates operation of a wireless access device.

FIG. 8 illustrates operation of channel allocation in an implementationof the wireless access device.

FIG. 9 is a flowchart of an example of an implementation of a methodperformed by a wireless access device.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of network 10 that uses a wireless accessdevice 100 to provide client devices (or “stations”), such as a laptopcomputer 20, access to data network services available on the Internet160. The wireless access device 100 is connected to a wired network 120,which provides the connection to the Internet 160. Depending on thenumber of stations and the size of the area of coverage, the network 10may include additional wireless access devices 130. A network managementsystem 120 may be used to configure and manage the wireless accessdevices 100, 130.

The wireless access device 100 in FIG. 1 has a substantially circularstructure 108 and includes an array controller 102, a plurality oftransceiver modules 110, and a network interface 114. The transceivermodules 110 contain one or more transceivers, radios, for example, andeach transceiver is connected to an antenna 112. The transceiver modules110 are also connected to the array controller 102, which operates toconfigure the transceiver modules 110 and manage any communicationsconnections involving the transceivers.

The wireless access device 100 shown in FIG. 1 has sixteen antennas 112.One of ordinary skill in the art will appreciate that any number ofantennas may be used. The antennas 112 that correspond to thetransceivers in the transceiver modules 110 are disposed near theperimeter of the substantially circular structure 108 of the wirelessaccess device 100. The antennas 112 are preferably directional antennasconfigured to transmit and receive signals communicated in a radialdirection from the center of the wireless access device 108. Eachantenna 112 covers a portion of the substantially circular areasurrounding the wireless access device 100 called a “sector” S_(i). Thetotal area covered by all of the sectors defines a 360° area of coverageof the wireless access device 100. This means that a station 20 locatedin a sector of the area of coverage would be able to communicatewirelessly with the antenna 112 corresponding with that sector.Multi-sector coverage is discussed in more detail below with referenceto FIG. 4.

The network 10 in FIG. 1 implements well-known standards and protocolsused to communicate over the Internet 160. The transceivers in thewireless access device 100 in FIG. 1 communicate with stations 20 inaccordance with the IEEE 802.11 standard (802.11a, 802.11b, 802.11g),which is incorporated herein by reference. The remainder of thisspecification describes operation of examples of the wireless accessdevice 100 in the context of systems that implement IEEE 802.11a, b, org. However, the present invention is not limited to systems thatimplement any particular standard.

The wireless access device 100 in FIG. 1 has four transceiver modules110. Each transceiver module 110 contains four transceivers, each ofwhich is programmable. In a preferred configuration, three of the fourtransceivers (shown in FIG. 1 with antennas labeled ‘a’) in eachtransceiver module 110 are designated to operate as 802.11a radios. Theremaining transceiver (shown in FIG. 1 with antenna labeled ‘abg’) maybe programmed to operate according to any of 802.11a, b, or g. Eachtransceiver is configured to operate on an assigned channel. The channelmay be one of the twelve channels available using the 802.11a standardor one of the fourteen channels available using the 802.11b/g standard.

The wireless access device 100 communicates with stations 20 wirelessly.The stations 20 may be any device enabled to communicate wirelessly withthe wireless access device 100 such as, without limitation, laptopcomputers, mobile telephones (for voice-over-LAN, or VOWLANapplications), personal digital assistants, handheld computers, etc. Inexamples described here, the stations are enabled to operate inaccordance with one or more of the 802.11 standards. When the station 20enters the coverage area of the wireless access device 100, it may senda request to connect to the Internet 160. The wireless access device 100may perform an authentication process in a login session. Onceauthenticated, the user of the station 20 may be connected to theInternet 160.

FIG. 2 is a block diagram of a transceiver module 210 that may beimplemented in the wireless access device 100 shown in FIG. 1. Thetransceiver module 210 includes four radios, one of which is an ‘abg’radio 220 and three of which are ‘a’ radios 222. All four radios 220,222 include an amplifier 230, a radio signal processor 240, and abaseband processor 250. The four radios 220, 222 communicate with atransceiver module interface 260, which allows the transceiver module210 to communicate with the rest of the wireless access device.

Each radio 220, 222 connects to an antenna 212, which transmits andreceives radio signals received from the amplifier 230. As describedwith reference to FIG. 1, the antennas 212 are directional antennas,which concentrate signal power in one direction. Directional antennascan therefore cover greater distances than omni-directional antennasused in typical wireless access devices. The multiple radios withradially disposed directional antennas advantageously provides a 360°coverage pattern that is larger than that of radios withomni-directional antennas used in current access points.

The baseband processor 250 processes the digital data that is eitherbeing received or transmitted by the radio 220, 222. The basebandprocessor 250 implements protocols required for such functions asassembling/disassembling payloads. The baseband processor 250 performsthe digital functions required to implement the 802.11 standard.Preferably, the baseband processor 250 is programmable and may beconfigured for any of the three standards (802.11a, 802.11b, 802.11g).One example of a baseband processor 250 that may be implemented is theAgere WL64040.

The radio signal processor 240 modulates signals to be transmitted anddemodulates signals that have been received. The radio signal processor240 is preferably programmable to implement either the modulationschemes specified by 802.11b/g or 802.11a. One example of a radio signalprocessor 240 that may be implemented is the Agere WL54040.

The amplifier 230 generates the radio signal to be transmitted by thetransceiver 220, 222 and amplifies signals being received by the antenna212. One example of an amplifier that may be implemented in thetransceiver module 210 is the SiGe Semiconductor SE2535L for the 5 GHzor 802.11a radios, and the SiGe Semiconductor SE2525L for the 2.4 GHz or802.11b/g radios.

In the transceiver module in FIG. 2, the amplifier 230, radio signalprocessor 240, and/or baseband processor 250 may be programmable so thatthe array controller 102 (in FIG. 1) may control the transceiver module200 in a manner that provides certain features. For example, the arraycontroller 102 (in FIG. 1) may control the amplifiers 230 in a mannerthat makes the coverage pattern of the wireless access device 102 largeror smaller depending on the needs of the implementation. In addition,the baseband processor 250 may communicate information (such as signalstrength) about the radio connection between the wireless access device100 and the stations 20.

It is noted that the following description refers to transceivers asradios. Those of ordinary skill in the art will appreciate that the term“radio” is not intended as limiting the transceiver to any particulartype.

FIG. 3 is a block diagram of an array controller 300 that may beimplemented in the wireless access device 100 shown in FIG. 1. The arraycontroller 300 includes a processor 310, a packet and queue controller320, a medium access controller 330, a radio interface 340, and a datanetwork interface 350.

The processor 310 provides computing resources to the wireless accessdevice. The processor 310 may be any suitable custom or commercialmicroprocessor, microcontroller, computing chip or other type ofprocessor. The array controller 300 also includes supporting circuitryfor the processor 310 such as clock circuitry, I/O ports, memory(including Read Only Memory, or ROM, Random Access Memory, or RAM, Flashmemory, Programmable Rom or PROM, etc.), direct memory access, etc. Theprocessor 310 may also manage a bus system for communicating with itssupport circuitry and with the packet and queue controller 320, datanetwork interface 350 and medium access controller 330. In one example,the processor 310 is a Motorola 8540 800 MHz CPU supported by 64 MBexpandable system FLASH memory, 128 MB DDR 333 expandable system RAM,and a serial interface (RS232-RJ45 connector). An optional securityco-processor may also be included.

The data network interface 350 includes input/output circuitry forcommunicating over a data network. The array controller 300 implementsstandards and protocols that allow for communication over the Internet.The data network interface 350 preferably allows for the highestpossible speed connection. In one example, the data network interface350 includes primary and secondary Gigabit Ethernet interfaces, a FastEthernet interface, and failover support between the Gigabit Ethernetinterfaces.

The packet and queue controller 320 handles receiver and transmitterqueues, performs DMA functions, resolves fragmentation, and performspacket translation. The medium access controller 330 provides all IEEE802.11 MAC services for transceivers. For the wireless access device 100in FIG. 1, the medium access controller 330 provides 802.11 MAC servicesfor as many as sixteen transceivers. Both the packet and queuecontroller 320 and the medium access controller 330 are preferablyimplemented as application specific integrated circuits (ASIC).

The array controller 300 performs the programmed functions that controlthe wireless access device 100 as an access point. Functions andfeatures of the operations that the array controller 300 performsinclude:

-   -   1. General implementation IEEE 802.11 Access Point        functionality.    -   2. Non-blocking packet processing from/to any radio interface.        In typical wireless access devices that employ a single,        omni-directional radio, a packet that is being transmitted may        block other packets from access to the medium. This may occur in        either direction. Stations typically transmit packets to an        access point when the medium is not busy. If the medium is busy        with packets from other stations, for example, the packet is        blocked. Similarly, the access point may be attempting to send a        packet to a station. If other packets are being sent to another        station, the original packet is blocked from access to the        medium. In the wireless access device 100, when a station is        blocked from communicating a packet to one radio, it may switch        to another radio that is not blocked. If the wireless access        device 100 is blocked from sending a packet via one radio, it        may switch to another radio.    -   3. Dynamic automatic channel assignment. The array controller        300 implements algorithms and/or other schemes for assigning        channels of the 802.11 standards to the multiple radios.        Channels are allocated to radios in a manner that reduces        adjacent channel interference (ACI).    -   4. Directional awareness of where a wireless station is in        geographic relationship to the wireless access device 100. The        array controller 300 receives information such as signal        strength, and for each station, may keep track of how the signal        strength changes over time. In addition, even if one radio is        locked in and “connected” to a station, another radio may        receive signals and thus, “listen” to the station. The signal        strength in relation to the specific radios gathering signal        information provide the array controller with sufficient        information to create a directional awareness of the location of        the wireless station.    -   5. Station mobility services whereby a station can instantly        roam from one sector to another without requiring        re-authentication of the station. As a wireless station moves in        the coverage area space of the wireless access device, the        signal strength sensed by the array controller changes. As the        signal strength of the station becomes weaker, the radio        associated with the adjacent sector locks in and “connects” with        the station without requiring re-authentication.    -   6. Wireless quality of service.    -   7. Enhanced load balancing of wireless stations.    -   8. Constant RF monitoring of channel conditions and security        threats    -   9. Wireless Security processing    -   10. Internal Authentication Server. Typically, authentication        takes place at a server or router that is wired to the access        points. In the wireless access device 100, authentication may be        done by the array controller 300.    -   11. Wired Networking protocol support.    -   12. System failover handling and error handling. Because sectors        overlap, when a radio fails, the adjacent radios may lock in        with stations being handled by the failed radio. In some        examples of the wireless access device 100, the array controller        300 may increase power to adjacent sectors to ensure coverage in        any area covered by the failed sector. In addition, when        multiple access devices are deployed, one wireless access device        may increase power and expand a sector to cover area left        without service when a radio fails in an adjacent wireless        access device.    -   13. System management functions.

As discussed above, examples of wireless access devices and systems thatemploy wireless access devices described in this specification (withoutlimitation) operate in the wireless LAN environment established by theIEEE 802.11 standardization body. The IEEE 802.11 standards including(without limitation):

-   -   IEEE 802.11, 1999 Edition (ISO/IEC 8802-11: 1999) IEEE Standards        for Information Technology—Telecommunications and Information        Exchange between Systems—Local and Metropolitan Area        Network—Specific Requirements—Part 11: Wireless LAN Medium        Access Control (MAC) and Physical Layer (PHY) Specifications    -   IEEE 802.11a-1999 (8802-11:1999/Amd 1:2000(E)), IEEE Standard        for Information technology—Telecommunications and information        exchange between systems—Local and metropolitan area        networks—Specific requirements—Part 11: Wireless LAN Medium        Access Control (MAC) and Physical Layer (PHY)        specifications—Amendment 1: High-speed Physical Layer in the 5        GHz band    -   IEEE 802.11b-1999 Supplement to 802.11-1999, Wireless LAN MAC        and PHY specifications: Higher speed Physical Layer (PHY)        extension in the 2.4 GHz band    -   802.11b-1999/Cor1-2001, IEEE Standard for Information        technology—Telecommunications and information exchange between        systems—Local and metropolitan area networks—Specific        requirements—Part 11: Wireless LAN Medium Access Control (MAC)        and Physical Layer (PHY) specifications—Amendment 2:        Higher-speed Physical Layer (PHY) extension in the 2.4 GHz        band—Corrigendum1    -   IEEE 802.11d-2001, Amendment to IEEE 802.11-1999, (ISO/IEC        8802-11) Information technology—Telecommunications and        information exchange between systems—Local and metropolitan area        networks—Specific requirements—Part 11: Wireless LAN Medium        Access Control (MAC) and Physical Layer (PHY) Specifications:        Specification for Operation in Additional Regulatory Domains    -   IEEE 802.11F-2003 IEEE Recommended Practice for Multi-Vendor        Access Point Interoperability via an Inter-Access Point Protocol        Across Distribution Systems Supporting IEEE 802.11 Operation    -   IEEE 802.11g-2003 IEEE Standard for Information        technology—Telecommunications and information exchange between        systems—Local and metropolitan area networks—Specific        requirements—Part 11: Wireless LAN Medium Access Control (MAC)        and Physical Layer (PHY) specifications—Amendment 4: Further        Higher-Speed Physical Layer Extension in the 2.4 GHz Band    -   IEEE 802.11h-2003 IEEE Standard for Information        technology—Telecommunications and Information Exchange Between        Systems—LAN/MAN Specific Requirements—Part 11: Wireless LAN        Medium Access Control (MAC) and Physical Layer (PHY)        Specifications: Spectrum and Transmit Power Management        Extensions in the 5 GHz band in Europe    -   IEEE 802.11i-2004 Amendment to IEEE Std 802.11, 1999 Edition        (Reaff 2003). IEEE Standard for Information        technology—Telecommunications and information exchange between        system—Local and metropolitan area networks Specific        requirements—Part 11: Wireless LAN Medium Access Control (MAC)        and Physical Layer (PHY) specifications—Amendment 6: Medium        Access Control (MAC) Security Enhancements    -   IEEE 802.11j-2004 IEEE Standard for Information        technology—Telecommunications and information exchange between        systems—Local and metropolitan area networks—Specific        requirements—Part 11: Wireless LAN Medium Access Control (MAC)        and Physical Layer (PHY) specifications—Amendment 7: 4.9 GHz-5        GHz Operation in Japan        All of the above-listed standards are incorporated herein by        reference.

Radios operating under 802.11 may operate in one of two frequency bands:the 2.4 GHz band and the 5 GHz band. The IEEE specifies multiplechannels within each band (see Table 1). Channels are defined asallocations of frequency spectrum with specified center frequencies andspacing. For example, in the 2.4 GHz band there are 14 defined channelsstarting at a center frequency of 2.412 GHz and incrementing up to 2.484GHz at 5 MHz intervals. Channels are considered overlapping if theirbands overlap above a certain power threshold. For instance, in the 2.4GHz region each channel operates with a frequency band of 12 MHz oneither side of the center frequency. So with 14 channels defined withcenter frequencies 5 MHz apart, several of them are overlapping. Infact, there are only three channels (channels 1, 6, and 11) that do notoverlap in the 2.4 GHz band. Their center frequencies are 2.412 GHz,2.437 GHz and 2.462 GHz.).

In the 5 GHz band, the IEEE Std. 802.11a-1999 defines 200 channels; eachchannel centered every 5 MHz from 5000 MHz to 6000 MHz. The 802.11astandard currently allows for 12 channels in the US. The 12 channelsprovided by 802.11a are non-overlapping channels. The FCC is expected toallocate 11 additional channels in the 5.47 to 5.725 GHz band. Those ofordinary skill in the art will appreciate that the channels describedherein are for purposes of illustrating an example and not intended asany limitation on the scope of the invention. Embodiments of the presentinvention that are designed to implement any part of the 802.11 standardmay use any set of channels specified by any part of the IEEE 802.11standard whether such channels are available now or in the future.

TABLE 1 IEEE 802.11 U.S. Radio Channel Assignments Channel NumberFrequency (MHz) IEEE 802.11 A (5.0 GHz Band) 36 5180 40 5200 44 5220 485240 52 5260 56 5280 60 5300 64 5320 149 5745 153 5765 157 5785 161 5805IEEE 802.11 B/G (2.4 GHz Band) 1 2412 2 2417 3 2422 4 2427 5 2432 6 24377 2442 8 2447 9 2452 10 2457 11 2462 12 2467 13 2472 14 2484

The wireless access device 100 in FIG. 1 assigns channels to the sixteenradios in a manner that enhances performance, throughput, coverage areaand capacity. Typical access points use one radio with a coverage areadefined by an omni-directional antenna and assigned to a single channel.Therefore, all of the users in the coverage area tune in to the samechannel in order to communicate with the access point. In the wirelessaccess device 100 in FIG. 1, each radio forms a different sectordefining a portion of a substantially circularly-defined coveragepattern. In addition, each radio is assigned a unique channel so that notwo radios in one device communicate over the same channel.

FIG. 4 is a diagram illustrating the formation of sectors by thewireless access device of FIG. 1. The wireless access device 100 has 16radios 412 divided into groups of four radios 412 mounted on each offour transceiver modules 410. An array controller 402 is located roughlyin the center of the wireless access device 100 where it connects witheach of the four transceiver modules 410 at inter-module connections408. The inter-module connections 408 contain communication paths (via abus or set of signal paths on a connector) that implement the interfacebetween the array controller 402 and the radios 412.

As discussed, each radio 412 contains a directional antenna configuredto establish a coverage area in a sector 450 that radiates out from thewireless access device 100. The radios 412 may be individuallycontrolled such that when they are all operating they may form acoverage pattern that surrounds the wireless access device 100. Thecoverage pattern created by the wireless access device 100 may besimilar to coverage patterns created by existing access points that useone radio radiating out of an omni-directional antenna. However, thewireless access device 100 in FIG. 4 uses sixteen radios 412 radiatingout of more powerful directional antennas to create a coverage patternarea that is significantly greater than that of a typical access point.In addition, the sectors 450 created by the radios 412 in the wirelessaccess device 100 advantageously overlap to provide features notcurrently available in typical access points. The radios 412 are alsoprogrammable such that they may be controlled to operate at power levelsthat allow for coverage patterns that are suited to the layout of theimplementation. Examples are discussed below with reference to FIGS.5A-E.

In FIG. 5A, a wireless access device 100 is implemented in animplementation I with all of the radios in the wireless access device100 configured to communicate with stations within a coverage area 502.The radios in the wireless access device 100 form sectors. A firstsector 530 is shown with an adjacent sector 540 along with an area ofoverlap 550 formed by the overlap of the first and second sectors 530,540. FIG. 5A illustrates one of many advantages that the wireless accessdevice 100 has over typical access points. The wireless access device100 includes programmable and configurable control over the operation ofthe radios on the wireless access device 100. When deployed, thewireless access devices 100 may be configured to create a coveragepattern that is suitable for by the exact implementation I. For example,in FIG. 5A, the coverage pattern 502 has been configured to conform tothe implementation I. The wireless access device 100 may be configuredsuch that the radios that create a set of coverage patterns 522, 524,526, 528, 530 that project towards a side 580 communicate signals at alower power limiting the extent of the coverage area created by eachradio. This is illustrated by a set of middle sectors 524, 526, 528covering less distance than outer sectors 522, 530, which cover thecorners or the implementation I along the side 580. This implementationI advantageously substantially limits the ability for a station toconnect from beyond the wall along the side 580 of implementation I.

FIG. 5B illustrates how the wireless access device 100 may be configuredto provide special features in a specific implementation. In FIG. 5B,the wireless access device 100 is implemented in a space 570 in whichthe resident desires to have wireless Internet access. The space 570 islocated with one side 590, which faces an open and public area fromwhich hackers or otherwise unauthorized users may attempt to gain accessto the Internet via the wireless access device 100. The wireless accessdevice 100 may be used to provide users in the space 570 with access tothe Internet while limiting access by those on the other side of 590.One way as illustrated in FIG. 5B is to place the wireless access device100 along the side 590 and turn off radios that would create sectors onthe other side of 590, and turn on the radios that create sectors in thespace 570. Such an implementation would yield a coverage pattern similarto the one shown in FIG. 5B.

FIG. 5C shows how the wireless access device 100 may be configured tolimit the affects of obstacles that may cause reflections in the radiosignals. Reflections in typical access points may cause multi-pathinterference. When radio signals reflect off of obstacles, thereflections may reach the station as different signals coming fromdifferent directions, or multiple paths. The wireless access device 100may be configured to avoid multi-path interference by configuring theradios to avoid generating sectors that could reach the obstacle. InFIG. 5C, the wireless access device 100 is shown generating sectors 520,540, but not generating any sectors in the direction of obstacle 575.

FIG. 5D illustrates how overlapping sectors may be used to provide radiofrequency failover so that stations do not lose connectivity when aradio fails, or is otherwise unavailable. In FIG. 5D, wireless accessdevice 100 has three radios creating a sector each (R1, R2, R3). In FIG.5E, the wireless access device 100 has lost the radio associated withsector R2. However, sectors R1, R2, R3 advantageously overlap. Thewireless access device 100 may switch stations in sector R2 that wereconnected via the radio that generated sector R2 to the radios thatcreated either of sectors R1 or R3.

FIG. 6A is a diagram of a wireless access device 100 of FIG. 1 labeledby radio type and number. Radios that communicate, or are configured tocommunicate, as 802.11a radios only are labeled ‘a.’ Radios that may beprogrammed or configured to communicate using 802.11a, b, or g radiosare labeled ‘abg.’ The twelve ‘a’ radios 610 (a1-a12) are assigned aunique one of the twenty-three channels available under the 802.11astandard. Three of the four ‘abg’ radios are assigned the threenon-overlapping channels available under the 802.11b/g standards. Thefourth ‘abg’ radio is implemented as an omni-directional radio in listenmode exclusively.

FIG. 6B shows coverage patterns formed by the different radio types onthe wireless access device. The twelve ‘a’ radios 610 each have acoverage area emanating in a sector that spreads out more than 30°. Thesectors of the twelve ‘a’ radios 610 may combine to form a substantiallycircular 802.11a coverage pattern 620. Preferably, the sectors arelarger than 30° in order to create overlap between the sectors, such asfor example, the overlap 650 between sectors 630 and 640. FIG. 6B alsoshows the three ‘abg’ radios 611 with the coverage area of more than120°. The sectors combine to provide a 360° coverage pattern. However,each sector is more than 120° to create overlap between the sectors. Thefourth ‘abg’ radio 613 is configured as an omni-directional radio ableto communicate in all directions. The fourth ‘abg’ radio 613 is used asa monitor or a sniffer radio in a listen-only mode. This radio listensto each channel in sequence to build a table of all stations and accessdevices. This table may be compared to an administrator controlled listof allowed stations and access devices. Stations and access devices notin the administrator controlled list are termed rogues. One functionperformed by the fourth ‘abg’ radio 613 is to detect unauthorizedstations in the coverage area.

FIG. 7 is a diagram of a wireless access device 700 connected wirelesslyto a plurality of stations 720 a-o via channels allocated to theplurality of radios a1-a12, afg1-afg4 on the wireless access device 700.The radios are labeled according to their type and radio numbers. Insidethe circles representing the radios are numbers identifying the channelsassigned to the radio. As shown, radios a1-a12 and afg1-afg4 areassigned channels as shown in Table 2 below:

TABLE 2 Radio No. Channel Frequency (MHz) A9 36 5180 A12 40 5200 A3 445220 A6 48 5240 A10 52 5260 A1 56 5280 A4 60 5300 A7 64 5320 A11 1495745 A2 153 5765 A5 157 5785 A8 161 5805 M — Monitor radio that canlisten on any abg channel abg1 1 2412 abg3 6 2437 abg4 11 2462

The radios in the wireless access device 700 are advantageously assigneddifferent channels. The radios in FIG. 7 and the array controller(described above with reference to FIG. 3) are housed within a singleenclosure tightly coupled by digital bus. The housing provides a centralcontrol point for the sixteen radios that is not tethered by any cabledbus.

The stations 720 a-o in FIG. 7 represents stations attempting to connectto the wireless access device 700. The arrows indicate the stations'ability to connect to a particular radio as well as the ability of thestation to communicate using the appropriate protocol (i.e. 802.11a, b,or g). To illustrate, station 720 a is a target wireless clientattaching to the wireless access device 700 using protocols specified by802.11a. Radios a5, a6, and a7 generate sectors that preferably overlapsuch that station 720 a may connect to either one of the three radios.Each radio is assigned a unique channel that does not overlap with anyother channel.

If the radio to which station 720 a fails, or is otherwise unable toprovide service to station 720 a, the array controller is able to switchthe connection to station 720 a over to one of the adjacent radios. TheIEEE 802.11a, b, and g protocols permit radios to “listen” to signalsbeing communicated with stations that are connected to another radio.The array controller may obtain data such as signal strength anddirectional awareness and other factors that allow it to determine whichradio is best suited to continue communicating with the station 720 a.

The wireless access device 700 is connected to a Gigabit Ethernet port780, which provides a direct connection to the user's network.

The radios in the wireless access device 700 are advantageously enclosedin proximity to one another providing the wireless access device 700with increased throughput, capacity and coverage area. In order tominimize interference between radios, each radio is assigned a uniquechannel. To further minimize the likelihood of interference, radios maybe assigned channels according to a channel allocation scheme.

To illustrate a scheme for allocating channels so as to minimizeinterference, reference is made to FIG. 8, which shows a top view of awireless access device 802 having 12 radios. A first radio 800 in thewireless access device 802 is between a first adjacent radio 804 and asecond adjacent radio 806. Adjacent to the second adjacent radio 806 isa fourth radio 810 and adjacent to the first adjacent radio 804 is afifth radio 808. Each of the twelve radios in the wireless access device802 is tuned to a unique IEEE 802.11a channel.

A channel is the 20 MHz band of frequencies surrounding a specifiedcenter or carrier frequency. The channel consists of 18 MHz of activelyused frequencies and 2 MHz of guard band. A channel number in the fiveGHz band is the number derived by subtracting 5 GHz from the channelcenter frequency and dividing the result by 5. Table 1 shows the channelnumbers and corresponding center frequencies for each channel as definedin the IEEE 802.11a and 802.11b/g standards.

With the radios in close proximity, the operation of the wireless accessdevice 802 may generate co-channel interference, which is a signalgenerated outside a given channel that lies in the adjacent channel orchannels. In the 802.11a bands, co-channel interference is that part ofthe transmission spectrum that lies between −10 MHz and −30 MHZ and orthat part of the transmission spectrum that lies between 10 MHz and 30MHZ. The wireless access device 802 in FIG. 8 advantageously implementsa scheme that minimizes co-channel interference.

In the wireless access device 802, the first radio 800 may be set to afirst channel. The adjacent channel is the 20 MHz band of frequencieslying just above or just below the subject channel. As an example,channels 36 and 44 are adjacent to channel 40. In order to minimizeinterference, the wireless access device 802 assigns channels to theradios without using adjacent channels. That is, if a channel isassigned to a radio, the wireless access device 802 avoids using anadjacent channel to that channel. To the extent the use of adjacentchannels cannot be avoided, an adjacent channel may be assigned with aradial separation of between 90° and 150°.

In one example implementation, a channel allocation scheme may start bysetting the first radio 800 (in FIG. 8) to a specific channel. The twoadjacent radios 804, 806 may then be assigned channels that are aminimum number (n_(ch)) of channels away. If n_(ch) is 4, the adjacentradios 804, 806 are assigned channels that are at least 80 MHz away. Thenext adjacent radios 808, 810 may then be assigned channels that are atleast 40 MHz or 60 MHz (a smaller number n_(eha)) away from the firstradio 800.

In one example channel mapping scheme, the radios of a twelve radiocircular array may be assigned to the twelve channels of the 802.11a1999 specification. If n_(ch)=16 and n_(cha)=12, co-channel assignmentis limited to radios placed at 90, 120 and 150 degrees, approximately25,248 mapping schemes may be generated. An example of one of thoseschemes is shown below in Table 3.

TABLE 3 Radio Number Channel No. 1 36 2 52 3 149 4 40 5 56 6 157 7 44 860 9 153 10 48 11 64 12 161

The maps can be generated once and stored in non-volatile memory for useas needed or can be generated on the fly by a recursive program runningon the array control computer. For example, a computer program may beimplemented that generates, in sequence, all possible channel assignmentfor a circular, arbitrary-sized array of radios and searches thepossible assignments for channel maps which have the largest possiblevalues of n_(ch) and n_(cha) while also avoiding the use of adjacentdata channels, where possible, and by limiting their positions, whenavoidance is not possible, to locations that fall between 90 degrees and150 degrees of radial separation. This process determines a number ofmap candidates sharing equally advantageous n_(ch) and n_(cha) values.The map to be used by the access device may then be selected at random,for example, using a random number generation function from the set ofequally advantageous maps.

The selected channel allocation map may be applied to the radios of thewireless access device 800 array.

Interference may also come from foreign associated stations (stationsassociated with other wireless access devices), other wireless accessdevices, or sources not related to the wireless access device. Anexample of a system for allocating channels in a multi-radio circularwireless access device may be extended to optimize performance in thepresence of other wireless access devices and/or wireless LAN accesspoints and/or foreign-associated clients and/or sources of radiointerference not emanating from wireless LAN devices. Several factorsand calculations should be defined.

First, the RSSI may be monitored by the wireless access device. The RSSIis the receive signal strength in DBm. For wireless access devices, thenumber falls between −30 DBm and −95 DBm with −30 DBm being thestrongest signal. The wireless access device may also determine a nonwireless access device signal duty cycle, which is the percentage oftime that the radio receives energy above −85 DBm from signal sourcesnot recognized as that of the wireless access device. The channel usagefactor is a number obtained from the calculation of [(Packet length/bitrate)*(100+RSSI)]+[(Non wireless access device Signal Duty Cycle)*70].The spectrum usage matrix is a tabulation of the channel usage factormeasured for each radio in an array of radios on each channelpotentially available for use by said radio. The channel map qualityscore is the number calculated for each possible channel mapping schemeby summing the channel usage factors for each radio measured on thechannel designated for that radio by the channel mapping scheme. Thenumber will lie between 0 (for no interfering signals on any channel)and 70 times the number of radios (for all channels experiencing severeinterference).

FIG. 9 is a flowchart 900 of an example implementation of a methodperformed by the wireless access device. As an example, when thewireless access device powers up (step 902), all radios in the wirelessaccess device may be tuned to the same channel (such as channel 36)(step 904). The radios all listen for signals from any source arrivingon this channel. Radios whose antennas are oriented towards the possibleemitting source will receive substantially more signal than those not sooriented. Each radio receives the signal (906). Each radio thendetermines a signal score, i.e. each radio's Channel Usage Factor, whichis recorded in a table (step 908). All of the radios are then tuned tothe next channel (step 912). The radios receive the signals (step 906)and each radio determines the channel usage factor for the channel(908), and expands the table of channel usage factors. The process isrepeated and each time, a check is performed to see if all of thechannels have been used (step 910). When all of the channels have beenused, the channel usage factors are tabulated in a spectrum usagematrix. The process continues by testing the spectrum usage matrixagainst a table of possible mapping schemes that provide approximatelymaximum isolation (step 914). The wireless access device then sets theradios to the channel scheme that is most appropriate for the situationof the environment.

Each possible allocation map is weighted by calculating its Channel MapQuality Score. The Channel Allocation Maps having the best Channel MapQuality Score is chosen. Several Channel Allocation Maps may share thesame Channel Map Quality Score and, therefore, be equally advantageous.The map to be used by the access device may then be selected at random,for example, using a random number generation function from the set ofequally advantageous maps.

The following illustrates one example of a process for allocatingchannels in a wireless access device.

Channel Allocation in a Wireless Access Device

Step 1:

-   -   Determine all possible channel maps (preferably using a        recursive computer program.)    -   Initialize the computer variable NoCoChannels to false.

Step 2:

-   -   Examine the first channel map and find the number of co-channels        that are used. (co-channels, or adjacent channels, are channels        that are 20 MHz away from any other channel.)    -   If this value is zero, set a computer variable: NoCoChannels to        true.    -   If this value is not zero, find the largest and smallest angles        between co-channels.        -   If the largest angle is greater than 150 degrees eliminate            this map from consideration and go to Step 3.        -   If the smallest angle is less than 90 degrees eliminate this            map from consideration and go to Step 3.    -   Find the lowest value of N_(ch) for any radio in the first        channel map this is the N_(ch) score for the first map.    -   Store this value in a computer variable: MaxN_(ch)    -   Find the lowest value of N_(cha) for any radio in the first        channel map this is the N_(cha) score for the first map.    -   Store this value in a computer variable: MaxN_(cha)

Step 3:

-   -   Examine a second channel map and find the number of co-channels        that are used.    -   If this value is zero, set the computer variable: NoCoChannels        to true    -   If this value is not zero, and the computer value NoCoChannels        is true eliminate this map from consideration and go to Step 4.    -   Otherwise, if this value is not zero, find the largest and        smallest angles between co-channels.        -   If the largest angle is greater than 150 degrees eliminate            this map from consideration and go to Step 4.        -   If the smallest angle is less than 90 degrees eliminate this            map from consideration and go to Step 4.    -   Otherwise, find the lowest value of N_(ch) for any radio in the        second channel map this is the N_(ch) score for the second map.    -   If the N_(ch) value is greater than the stored value of        MaxN_(ch) replace MaxN_(ch) with this larger value and also find        the lowest value of N_(cha) for any radio in the second channel        map this is the N_(cha) score for the second map. Store this        value in a computer variable MaxN_(cha)    -   If the N_(ch) value is equal to the stored value of MaxN_(ch)        find the lowest value of N_(cha) this is the N_(cha) score for        the second map. Store this value in a computer variable        MaxN_(cha)    -   If the N_(ch) score is less than MaxN_(ch) do not evaluate        N_(cha) and eliminate this map from consideration

Step 4:

-   -   Examine the next channel map and find the number of co-channels        that are used.    -   If this value is zero set the computer variable NoCoChannels to        true    -   If this value is not zero and the computer value NoCoChannels is        true eliminate this map from consideration and go to Step 5.    -   Otherwise if this value is not zero find the largest and        smallest angles between co-channels.        -   If the largest angle is greater than 150 degrees eliminate            this map from consideration and go to Step 5.        -   If the smallest angle is less than 90 degrees eliminate this            map from consideration and go to Step 5.    -   Otherwise, find the lowest value of N_(ch) for any radio in the        channel map this is the N_(ch) score for the map.    -   If the N_(ch) score is greater than the stored value of        MaxN_(ch) replace MaxN_(ch) with this larger value and also find        the lowest value of N_(cha) for any radio in the this channel        map this is the N_(cha) score for the map. Store this value in        the computer variable MaxN_(cha) and eliminate all previously        examined maps from consideration.    -   If the N_(ch) value is equal to the stored value of MaxN_(ch)        find the lowest value of N_(cha) this is the N_(cha) score of        the map. If it is greater than the stored value of MaxN_(cha)        replace MaxN_(cha) with this value and eliminate all previously        examined maps from consideration.    -   If the N_(ch) score is less than MaxN_(ch) do not evaluate        N_(cha) and eliminate this map from consideration.

Step 5:

-   -   Repeat Step 4 for each of the many (usually many thousands) of        possible channel maps. The results of this iterative process        are:        -   If any channel map does not use co-channels then all maps            having co-channels will be eliminated from consideration.        -   MaxN_(ch) will grow to be the largest possible value for an            N_(ch) score MaxN_(cha) will grow to be the largest possible            value for an N_(cha) score among maps having the largest            possible N_(ch) score.        -   All channel maps whose N_(ch) score is not equal to            MaxN_(ch) and whose N_(cha) score is not equal MaxN_(cha)            will be eliminated from consideration.    -   The result of this process yields only the most advantageous        channel maps (that is, those having the largest N_(cha) from        among those having largest N_(ch) score). There may be many        channel maps sharing the same most advantageous scores.

The chosen Channel Allocation map is applied to the radios of thewireless access device.

Referring to FIG. 8, the wireless access device 802 is capable ofutilizing the error vector measurement (“EVM”) data in improving theperformance of the radios in the wireless access device 802. It isappreciated by those skilled in the art that the EVM is not a functionof the ambient conditions, and that the EVM is a performance measuredefined by the specification of IEEE 802.11.

In an example of operation, the first radio 800 may transmit a signalthat is received by any of the other radios in the wireless accessdevice 802. As an example, if a second radio 804 receives thetransmitted signal, the second radio 804 may calculate the EVM of thesecond radio by comparing the received signal (from the transmittedsignal) at the second radio with the known characteristics of thetransmitted signal at the first radio. This method compensates forvariations in gain characteristics of the different amplifiers andreceivers in the wireless access device 802 by providing a comparison ofthe radios based on the measured EVM. This comparison may allow for amaximum allowable transmit power to be varied to each radio circuit toallow for the highest transmit rates for the EVM. The EVM for each radiomay be stored in a table in the memory of the wireless access device 802and used for improving the performance of the radios.

The EVM for each radio may be used for channel allocation in mannersimilar to the manner in which the Channel Usage Factor is used in theexample described with reference to FIG. 9. The EVM may be comparedagainst a predefined table in the wireless access device 802 asdescribed above. Instead of calculating the channel usage factor, theEVM may be calculated for each radio at each channel for a signaltransmitted by each of the other radios. Once these values are known,EEPROMs may be programmed with the information and included in eachradio circuit. The EVM values may be tested against possible mappingschemes that provide approximately maximum isolation. The wirelessaccess device 802 then sets the radios the channel scheme that is mostappropriate for the characteristics of each radio.

Although the controller 300 depicted in FIG. 3 uses memory, one skilledin the art will appreciate that a substantial part of systems andmethods consistent with the present invention may be stored on or readfrom other machine-readable media, for example, secondary storagedevices such as hard disks, floppy disks, and CD-ROMs; a signal receivedfrom a network; or other forms of ROM or RAM either currently known orlater developed. Further, although specific components of wirelessaccess device 100 are described, one skilled in the art will appreciatethat a network access device suitable for use with methods, systems, andarticles of manufacture consistent with the present invention maycontain additional or different components.

The foregoing description of an implementation has been presented forpurposes of illustration and description. It is not exhaustive and doesnot limit the claimed inventions to the precise form disclosed.Modifications and variations are possible in light of the abovedescription or may be acquired from practicing the invention. Forexample, the described implementation includes software but theinvention may be implemented as a combination of hardware and softwareor in hardware alone. Note also that the implementation may vary betweensystems. The claims and their equivalents define the scope of theinvention.

What is claimed is:
 1. A method for allocating channels in a wirelessaccess device having a plurality of radios capable of operating on aplurality of channels, the method comprising: initially tuning each ofthe plurality of radios to a selected same one of the plurality ofchannels; transmitting a signal at the selected same channel from atransmitting one of the plurality of radios; receiving the signal at theselected same channel on the plurality of radios that are not thetransmitting radio; determining an error vector measurement (“EVM”) foreach one the plurality of radios that are not the transmitting radio;storing the EVM for each one of the plurality of radios that are not thetransmitting radio for the selected same channel for the transmittingradio; selecting a next one of the plurality of radios to transmit thesignal at the same selected channel; repeating the steps of transmittingthe signal at the selected same channel, receiving the signal at theselected same channel, determining the EVM, storing the EVM, andselecting the next radio until each one of the plurality of radios hastransmitted the signal at the same selected channel; tuning each of theplurality of radios to another one of the plurality of channels;repeating the steps of transmitting the signal at the selected samechannel, receiving the signal at the selected same channel, determiningthe EVM, storing the EVM, selecting the next radio, and tuning theplurality of radios to the other one of the plurality of channels untileach channel has been used; and testing the EVM scores against a tableof mapping schemes to determine maximum isolation.
 2. A method accordingto claim 1 where the EVM scores for each radio at each channel is storedin memory for use in determining highest transmit rates by varying amaximum allowable transmit power in each radio.
 3. A method according toclaim 1 where the step of calculating the EVM comprises: at each one ofthe plurality of radios that is not transmitting the signal at theselected same channel, determining characteristics of a received signal;retrieving characteristics of a transmitted signal at the selected samechannel; comparing the characteristics of the received signal with thecharacteristics of the transmitted signal; determining the EVM based onthe comparison.